The CN is an important factor in determining the quality of diesel fuel, but not the only one; other measurements of diesel fuel's quality include (but are not limited to) energy content, density, lubricity, cold-flow properties and sulfur content.
[7] In North America, most states adopt ASTM D975 as their diesel fuel standard and the minimum cetane number is set at 40, with typical values in the 42-45 range.
[12] Dimethyl ether is a potential diesel fuel as it has a high cetane rating (55-60) and can be produced as a biofuel.
Another reliable method of measuring the derived cetane number (DCN) of diesel fuel is the Ignition Quality Tester (IQT).
Fuel is injected into a constant volume combustion chamber at approximately 575 °C and 310 psi (21 bar).
The time between the start of injection and the recovery of the combustion chamber pressure to 310 psi (21 bar) is defined as the ignition delay.
Because of the reproducibility, material cost, and speed of the IQT, this has been the definitive source for DCN measurements of fuels since the late 2000s.
Fuel is injected into a constant volume combustion chamber in which the ambient temperature is approximately 575 °C.
The fuel's derived cetane number can then be calculated using an empirical inverse relationship to ignition delay.
Another statistic used by fuel-users to control quality is the cetane index (CI), which is a calculated number based on the density and a distillation range of the fuel.
These days most oil companies use the '4-point method', ASTM D4737, based on density and 10% 50% and 90% recovery temperatures.
The industry standards for measuring cetane number are ASTM D613 (ISO 5165) for the CFR engine, D6890 for the IQT, and D7170 for the FIT.